1. Technical Field
This invention relates to a fault management system for managing faults in the terminating circuits of a communications network and also to a method of operating such a fault management system.
2.Related Art
A conventional communications network comprises a relatively small number of interconnected main switches and a much larger number of local switches, each of which is connected to one or two of the main switches. The local switches are connected to the terminating circuits of the network and the far ends of these circuits are connected to terminal equipment such as telephone instruments provided for users of the network. The network formed from the main switches and local switches is known as the core network while a network formed from the terminating circuits is known variously as an access network or a local loop. In this specification, it will be referred to as an access network. Some terminating circuits are connected to a remote concentrator, which may or may not have switching capability. The remote concentrator is then connected to a local switch. In this specification, the term “local switch” is to be interpreted to cover both local switches and remote concentrators.
In a conventional access network, each terminating circuit is formed from a pair of copper wires. Typically, each pair of copper wires passes through a series of nodes (or network elements) between the local switch and terminal equipment. Examples of such nodes are primary cross-connect points, secondary cross-connect points, distribution points (DPs), cable nodes and joints.
Recently, optical fibres have been used to carry terminating circuits in access networks. In a modern access network, both pairs of copper wires and optical fibres are used to carry the terminating circuits. Where a terminating circuit is carried by an optical fibre, the circuit will typically pass through several nodes between the local switch and the terminal equipment. At each node, the incoming fibre from the local switch is split into a group of outgoing fibres which branch out in various directions. Where a terminating circuit is carried by an optical fibre from the local switch, the last part of the circuit may be carried by a pair of copper wires. Unfortunately, terminating circuits are prone to faults. In the case of a terminating circuit carried by a pair of copper wires, examples of such faults are disconnection, a short circuit between two wires of a pair of wires and a short circuit between one of the wires and earth. In the case of a conventional access network formed from pairs of wires, the causes of the faults include ingress of water into a node and also physical damage to a node.
When a customer reports a fault, the terminating circuit may be tested so as to identify the cause of the fault. The fault can then be repaired. However, until the fault is repaired, the user suffers a loss of service. It is known how to perform a set of circuit tests on each terminating circuit in an access network on a routine basis, for example nightly. Such routine tests can detect a fault on a terminating circuit. The fault can then be repaired, possibly before the user of the terminating circuit notices a loss of service. It is also known to measure the operational quality of individual nodes of an access network. Where the operational quality of a node is poor, it is likely that faults will develop in terminating circuits passing through the node. However, lines run though a number of nodes before terminating and so as a result, locating the node from which potential faults emanate is difficult and so efficient preventive maintenance is difficult.